An influential US Senator warned Thursday that US-Russia relations will be "strained for some time" but urged speedy efforts to extend a nuclear cooperation accord that expires December 5.

"The foundation of the US-Russian strategic relationship is at risk of collapsing in less than nine months," Senator Richard Lugar, the top Republican on the Senate Foreign Relations Committee, said in a statement.

At issue is the verification regime for the 1991 START nuclear pact, which committed Moscow and Washington to cut their arsenals, including reducing missiles to a maximum of 1,600 and warheads to no more than 6,000.

"We should carefully set priorities. Solidifying the START verification regime must be the primary focus," Lugar said as the committee opened a hearing on efforts to thaw chilly US-Russia relations.

In early March, US Secretary of State Hillary Clinton said after meeting with her Russian counterpart, Sergei Lavrov, that both sides agreed renewing the accord was "of the highest priority."

Lugar, one of the two US architects of a program aimed at safeguarding Moscow''s post-Soviet nuclear stockpiles, cautioned against expecting too much from efforts to ratchet up US-Russia cooperation on key issues.

"We should recognize that US-Russian relations are likely to be strained for some time," said the Indiana senator, his party''s leading foreign policy voice, adding: "We should be realistic in assessing the prospects for cooperation."